Sports-related mild traumatic brain injury (MTBI or concussion) is an important public health problem because of the high incidence of these injuries, the relative youth of those being injured with possible long term disability, the danger of cumulative effects from repeat incidences, and ineffective strategies for prevention. We propose to develop and validate a quantitative model of head impact acceleration that enables translational research and development of new clinical and therapeutic techniques to reduce the incidence and negative effects of MTBI. Experimental, clinical and product development projects among team members will allow hypothesis-driven research specific to the underlying pathomechanics and clinical sequelae of MTBI. Crucial to the study of the pathomechanics of concussion is the acquisition of actual head accelerations and exposures due to impact. Head Impact Telemetry System (HIT System) technology was previously developed and validated for measuring head impact accelerations in the field. This technology will, for the first time, enable prospective studies of biomechanical, clinical, and neuropsychological data in human subjects with closed head injury, allowing for direct measurement of injury parameters and their clinical consequences. Within a study population of collegiate football players and male and female collegiate hockey players, the three specific aims of this proposal are: 1) improve HIT system for large-scale recording, storage, and retrieval of on-field head impact acceleration data, 2) quantify head impact acceleration using HIT system to test hypotheses on the impact tolerance to MTBI injury and whether cumulative impacts or gender influence these tolerances, and 3) correlate head impact acceleration with clinical variables related to MTBI to test the hypothesis that increased head acceleration increases short-term measures of brain injury for concussed players relative to matched controls using validated sideline and clinical tools including standardized sideline assessments, neuropsychological testing, and fMRI. The results of these studies will provide the scientific basis for achieving long-term goals to develop and deploy novel strategies to improve detection, prevention, reduce the incidence, and improve treatment of MTBI.